The Rail Environment: A Challenge For Gnss

This chapter describes the foundations and principles of railway signalling systems and their main key elements and provides an accurate description of the main European Rail Traffic Management System (ERTMS) properties that can be affected by the introduction of the GNSS technology. In order to bring the readers to understand the complexity of the railway environment and the main differences with respect to civil aviation and maritime environments, Sects. 6.3.1 and 6.3.2 provide an overview of the applicable European Commission Regulations and of the complete Control-Command and Signalling System suitable for obtaining the Single European Railway Area, Sects. 6.3.3 and 6.3.4 outline the reference ERTMS System Architecture with emphasis on the interfaces and the functions to guarantee the interoperability requirements, and Sects. 6.3.5 and 6.3.6 accurately describe the ERTMS dependability requirements such as safety, reliability and availability along with the related reference Mission Profile. Furthermore, Sect. 6.4 describes the current process for assessing the conformity of a single ERTMS constituent and for verifying the ERTMS Command and Control and Signalling Subsystems. Finally, Sect. 6.6 provides a quick description of the on-board train environment with respect to radio frequency interferences, multipath and non-line-of-sight conditions to outline how these phenomena, considered negligible in the civil aviation environment, have a critical role in the railway environment.Note: The methodologies, the algorithms and the integrity concept to cope with Safety-of-Life applications described in the first part of the book will be tailored for the rail application throughout this chapter and the following one. This chapter brings the reader to understand the complexity of the rail environment and the basic current principles for determining the safe train position. Refer to the glossary at the end of this book for a quick access to the definition of some railway terminology [1] that is extensively used in the explanation of these principles. Instead, the next chapter will describe the concept of Virtual Balise, proposed for the introduction of the GNSS technology, and the possible enhanced ERTMS architecture suitable for a safe implementation of this concept. Many of the concepts and techniques described in this chapter and in the first part of the book will be tailored based on the Virtual Balise concept. The enhancement of the ERTMS standard for introducing the GNSS technology shall have to guarantee both the backward compatibility with existing ERTMS solutions and the interoperability requirements; however, as the definition of this standard evolution is still in progress, the tailored solution described in Chap. 7 must be considered as a consolidated and mature working framework only. This framework is based on the experience gained in many important R&D projects such as ESA-sponsored 3InSat [2] and SBS [3] projects, and GSA-sponsored ERSAT-EAV [4], RHINOS [5] and STARS [6] projects.